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The XPhase architecture implements feed-forward voltage mode control with modified type 3 compensation and trailing edge modulation in conjunction with adaptive voltage positioning. It permits the controller to automatically adapt to variations in the input voltage at each phase, as well as reduce voltage variation during load transient with minimal power loss at heavy load. Furthermore, by using good techniques, the controller can be tailored to attain a loop response as fast as 200ns or better. The result is impressive load transient response with minimal output capacitance. Thus, it sets a new benchmark in load line tolerance, beating Intel’s VR10 load line requirements.
Another novel feature unique to XPhase control is body braking. This patent pending control technique turns off the synchronous rectifier MOSFET in response to a significant decrease in load current. The synchronous rectifier’s lossy body diode conducts the inductor current, thereby increasing the voltage across the inductor. The result is nearly 2X improvement in the inductor slew rate. Besides permitting the use of larger inductor values and improving efficiency, body braking also helps in lowering output capacitor requirements. Figure 2 compares the load current step down response of a standard 4-phase buck converter against a similar solution with XPhase body braking. The curve shows a spike in the output voltage of the standard multiphase buck converter during the load step decrease, which is controlled in the XPhase buck converter with body braking.
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